Metal hardening

[blacksmithden]

Ok...I'm a total novice when it comes to making gun parts and I'm just starting into the whole gunsmithing thing. A friend has brought me a couple of trigger parts from his dads old gun and asked me to make new ones. These are pretty worn out and the hammer won't always lock back in the cocked position anymore.

My issue isn't making them...it's what grade of steel are trigger parts made out of ? Do they need to be hardened after manufacturing ? I was thinking of making them out of a piece of mild steel bar stock, and them heating them up with a torch and dunking them in oil. Thoughts ? Advice ? Ideas ? Thanks in advance guys....any help will be appreciated.

 

[DMS]

Not being a gunsmith, and not knowing much about the particulars of material choice, I can say that using mild steel like that is not going to get you a hardened part. You will either need to pack-carburize the part if it is mild steel, or make it out of something with a higher carbon content.

 

[blacksmithden]

Not being a gunsmith, and not knowing much about the particulars of material choice, I can say that using mild steel like that is not going to get you a hardened part. You will either need to pack-carburize the part if it is mild steel, or make it out of something with a higher carbon content.

:whiteflag: What...too soon ? LOL !

I am SO not up on carbon contents, grades of steel, and such.....I'm trying to remember stuff from 30 years ago, but the grey matter is a bit tougher to reactivate these days....what do you think I should try ? Would you be able to give me a number...something I can walk into the metal store and ask for ? I'll do a search on what pack-carburizing is in the mean time. Thanks.

 

[cdhknives]

If you just want a easy to find hardenable steel for higher wear parts like triggers and sears, ask for 4140 or even O-1 tool steel.

Both require a tempering cycle to draw it back to spring hardness. Both require oil quenching, but good old ATF works fairly well.

http://www.anvilfire.com/FAQs/heat-treating-4140.php

EDITED BY GEORGE WILSON:Sorry,4140 is not a suitable steel for making triggers from. Even if a home shop person gets it hardened fully,that is only 54 R.C.. Then it must be tempered. Tempering at 600º will give only 47 R.C.,which is softer than a really poor wood working saw.(Good ones are more like 52 R.C.,and still can be filer sharpened). Any tempering at all will reduce the hardness to a dangerously soft level.

01 is a very suitable steel for making a trigger sear,or a hammer if it is also necessary. I would not draw it back much softer than 57 R.C.. If the sear wears out,the gun can go off all by itself,or if a semi auto,can go full auto. We need to be extremely careful about giving advice when it comes to making gun parts.

 

[DMS]

4140 is nice stuff to work with. Bit more expensive than plane Jane 1018, but 4x as strong and hardenable.

For the steels sold in the US (Europe uses a different identification scheme), the last two digits indicate the carbon content in 100ths. So 4140 has approximately 0.4% carbon, 1018 has 0.18% carbon. To be hardenable, you want at least 0.4% carbon, so something like 4140, 1095, 1045, or O1 (doesn't use the 4 digit numeric code, but carbon content is about 0.95% carbon) would all work.

EDITED BY GEORGE WILSON:See the above post: 4140 is not a suitable steel for making triggers or hammers,or any part that can wear out and make the gun dangerous.

 

[Ray C]

Agree on all points...

My personal preferance is 4140 and I feel it's easier to heat treat than 1045 or 1095 since it's less prone to cracking, is considerably tougher stuff -and does not decarburize as easily.

The very simplified recipe for 4140 is: Form the part, heat to 1550F (bright red, almost orange) and dunk in oil with plenty of agitation until it's warm to the touch. Next, warm the part up to anywhere from 400 to 1000 F, and let it gradually cool in standing air. That last step is the temper. The hotter you heat the piece, it will end up softer (but less brittle). Tempering at low temperatures leaves the piece hard and brittle. Tempering at 600 is a good happy-medium.

For pieces where the smallest cross section is larger than say, 3/8" (roughly) the heat treat and temper times must be held for 30 minutes and up to 1 hour for each 1" of additional cross section. For those smaller pieces, you can get away with heating and holding for about 5 minutes. The real trick is knowing when you've hit 1550. It's very critical to reach that temperature or, the whole process will do you little good -and may even leave the metal much softer than when you started.


Ray

EDIT: Ray has asked me to clarify that he is agreeing that 4140 is a better metal for heat treating than 1018,not that 4140 is a suitable steel for making triggers or hammers that have sears that can wear out from insufficiently hard steel.

4140 is nice stuff to work with. Bit more expensive than plane Jane 1018, but 4x as strong and hardenable.

For the steels sold in the US (Europe uses a different identification scheme), the last two digits indicate the carbon content in 100ths. So 4140 has approximately 0.4% carbon, 1018 has 0.18% carbon. To be hardenable, you want at least 0.4% carbon, so something like 4140, 1095, 1045, or O1 (doesn't use the 4 digit numeric code, but carbon content is about 0.95% carbon) would all work.

 

[cdhknives]

Plain old 10xx steels require very fast quenching...water quench...to get good hardening deep into the metal. Sometimes that is desirable, often not. It often cracks, especially at sharp corners (stress risers) due to the severity of water quenching. It is quite cheap though.

4140 is an alloy steel, and for our purposes here the extra alloy gives better toughness and better hardening characteristics. You can cool it slower via oil quench and it will still harden through. Ditto O-1, though as a tool steel O-1 is held to better controls on contaminants, tighter alloy % specs, etc. as well making it 'better' and more costly. for the quantities to make a couple of triggers, the cost is trivial. O-1 is also usually found precision ground, so you can get the thickness you want (if you want a standard size) already ground nice and parallel. That helps a lot if you don't have a surface grinder and want a number of uniform parts.

EDITED BY GEORGE WILSON:Once again,4140 is not a suitable steel for making triggers from,or hammers. If this continues,I will have to start deleting posts due to safety reasons. We do not want anyone getting shot because incorrect advice was given here. 01 is a very suitable metal for triggers.

 

[wyldboar]

1018 would work and then case harden with KASEINITE or some other surface hardening compound




EDITED BY GEORGE WILSON: Kasenite is no longer available. It only was good for shallow case hardening anyway. For a trigger sear,you need deeper hardening so the sear does not wear out and the gun goes off by itself.

If you want deeper casehardening,use aquarium charcoal and a CLOSED crucible. Embed the part(S) in charcoal,and heat the crucible up red hot for an hour AFTER it gets red. I hardened common nails in a crucible with bone meal by heating the crucible red hot for 2 hours. The nails were just used to test the depth of the case. Every once in a while,I'd pull out a 4" nail and break it. I got 1/32" deep hardening after 2 hours. Then,I knew the actual parts I wanted that were also in the crucible were hardened that deep,so I quenched them and tempered them.

 

[blacksmithden]

Great stuff guys !!!!Thanks for all the info !!! I'll be going to the metal store tomorrow, but then have to head out of town with the family for the weekend so no playing in the shop for a few days. I'm planning on reading up on various types of steel when we're on our way to Calgary. I did learn a lot of this WAY back, but I've completely forgotten most of it now. Hopefully some of it comes back. THANKS AGAIN. You guys are the best !

 

[Hawkeye]

For an in-depth tutorial on heat treating, I ordered Workshop Practice Series #1 - Hardening, Tempering and Heat Treatment on-line. Not much more than 100 pages. I learned a lot from reading through it, including the basics of why it all works.